Django WebSocket Channel Redis

?目的：实现有新模型创建的时候自动通知浏览器刷新模型列表
本例子实现了，在admin新上传一个文档的时候，通知客户端

盗用一张介绍Websocket的图

1. 建一个 Django 项目，或者下载我的 Django base 项目

git clone git@github.com:chunkai-meng/base-django.git

2. 安装 channels 和 channels-redis

cd base-django/proj
pipenv install channels channels-redis

docker run --name websocket-redis -p 6379:6379 -d redis

3. 加入 Channel 到 INSTALLED_APPS & 添加 CHANNEL_LAYERS 到 settings

# settings.py
INSTALLED_APPS = [
    'channels',
    # ...
]

....
ASGI_APPLICATION = "proj.routing.application"

CHANNEL_LAYERS = {
    "default": {
        "BACKEND": "channels_redis.core.RedisChannelLayer",
        "CONFIG": {
            "hosts": [("localhost", 6379)],
        },
    },
}

4. Code files

1. proj/routing.py - already mentioned in settings.py as ASGI_APPLICATION, which direct all the WebSocket request to the right consumers.

from channels.routing import ProtocolTypeRouter, URLRouter
from django.urls import path
from notification.comusers import NotificationConsumer

application = ProtocolTypeRouter({
    "websocket": URLRouter([
        path("notifications/", NotificationConsumer),
    ]),
})

2. notification/consumers.py - an action handler to establish handshake, receive and send msg to the client.

from channels.generic.websocket import AsyncJsonWebsocketConsumer


class NotificationConsumer(AsyncJsonWebsocketConsumer):
    async def connect(self):
        await self.accept()
        await self.channel_layer.group_add('gossip', self.channel_name)

    async def disconnect(self, code):
        await self.channel_layer.group_discard('gossip', self.channel_name)

    async def name_gossip(self, event):
        await self.send_json(event)

3. document/signals.py - a hook to send msg to the channel listened by consumer

from .models import Document
from django.db.models.signals import pre_save
from django.dispatch import receiver
from asgiref.sync import async_to_sync
from channels.layers import get_channel_layer


# hook to be called whenever a Document is saved.
@receiver(pre_save, sender=Document)
def notify_post_save(sender, **kwargs):
    if "instance" in kwargs:
        instance = kwargs["instance"]
        channel_layer = get_channel_layer()
        async_to_sync(channel_layer.group_send)(
            "gossip", {
                "type": "name.gossip",
                "event": "New Document",
                "sender": instance.owner.username,
                "message": instance.name
            }
        )

4. document/apps.py - register the signal when the app is ready

from django.apps import AppConfig


class DocumentConfig(AppConfig):
    name = 'document'
    verbose_name = 'Documents'
    def ready(self):
        import document.signals

个人理解：

1. Channel 是个管道，用来异步传递消息，需要 pip install
2. Redis 是后端，要启动好，并且 localhost:6379 能访问，反正要跟设置里的一致
3. Settings 里定义了 WebSocket 的请求都去找 routing.py
4. routing.py 里定义了 一个 consumer 路径在 notifications/ 所以一会 WebSocket 客户端要去访问这里
5. NotificationConsumer 就是一个标准的 Consumer
6. notify_post_save 是一个测试用的钩子，目的是异步的出发消息发送到 Channel，然后回给客户端

有不对的地方欢迎留言